cannoneer vs machine gunner

cannoneer and machine gunner both are nouns.

Word	Noun	Adjective	Verb	Adverb
cannoneer	Yes	No	No	No
machine gunner	Yes	No	No	No

As nouns, cannoneer and machine gunner are synonyms defined as:

Other synonyms of cannoneer include artilleryman, gunner.

cannoneer (noun)	machine gunner (noun)
a serviceman in the artillery	a serviceman in the artillery